The invention relates to a safety device means for a passenger conveyor system, more particularly an escalator or travelator, including a main drive shaft mounting the return elements for the transport chains of the steps or pallets, a further shaft containing the return elements for the handrails as well as at least one gear unit connecting the main drive shaft to the shaft, the drive power of at least one drive unit arranged external to the return elements being translatable via transport means to the main drive shaft.
It is known in general that passenger conveyor systems, such as escalators and travelators having external main drives, make use of safety brakes in the form of sprag brakes, disc brakes or the like in the region of the associated driven elements. Due to lack of a reduction in translation, high flyweight and low rotary speed of the driven elements (approx. 10-20 rpm) in conjunction with a constantly set braking moment corresponding to the level of the load moment anticipated, shock engagement of the brake is often encountered in the case of untoward sudden events such as chain breakage, overspeed and reversal of rotation.
Pertinent safety regulations view a stopping distance of min. 200 mm and max. 1000 mm as being adequate for passenger conveyor systems at a travelling speed of roughly 0.5 m/s. In the prior art, difficulties associated with the braking moment corresponding to the load moment are only encountered in a light load situation, i.e. with only a few passengers on the escalator or travelator, to the effect that the travelator or escalator is abruptly halted after a delay of approx. 50-80 mm due to sudden engagement of the brake, resulting in the passengers risking a fall and possible serious injury. The components too, of the passenger conveyor system risk being severely loaded by this abrupt halt, especially in a light load situation, so that here too considerable damage may result.
Brakes as put to use hitherto with external drives are complicated, expensive and bulky in design.